1. Field of the Invention
The present invention relates to an automatic sound field correcting device which automatically corrects a sound characteristic in an audio system having a plurality of speakers.
2. Description of Related Art
For an audio system having a plurality of speakers to provide a high quality sound space, it is required to automatically create an appropriate sound space with much presence. In other words, it is required for the audio system to automatically correct sound field characteristics because it is quite difficult for a listener to appropriately adjust the phase characteristic, the frequency characteristic, the sound pressure level and the like of sound reproduced by a plurality of speakers by manually manipulating the audio system by himself to obtain appropriate sound space.
So far, as this kind of automatic sound field correcting system, there is known a system disclosed in Japanese Patent Application Laid-open under No. 2002-330499. In this system, for each signal transmission path corresponding to plural channels, a test signal outputted from a speaker is collected, and a frequency characteristic thereof is analyzed. Then, by setting coefficients of an equalizer provided on the signal transmission path, each signal transmission path is corrected to have a desired frequency characteristic.
In a normal automatic sound field correcting system, the above-mentioned frequency characteristics correction is performed a plurality of times. Namely, a measurement sound is outputted from a speaker once, and a test signal is collected by a microphone. Then, an equalizer coefficient is set once. After setting of the equalizer coefficient, i.e., after the first correction, the test signal is outputted from the speaker again, and the test signal is collected by the microphone. The frequency characteristics correction is repeated plural times. Thereby, an error due to interference of the equalizer between frequency bands of a plurality of signal transmission paths, and a difference of characteristics between a frequency analyzing filter and an equalizer are absorbed. Concretely, the above-mentioned frequency characteristics correction process is repeated four to six times, and the final equalizer coefficient is determined.
However, as described above, since the operation of outputting the test signal from the speaker and collecting the outputted sound by the microphone is executed in each of a plurality of frequency characteristics correction processes, a time necessary for the frequency characteristics correction problematically becomes longer. The reasons are as follows. First, the test signal is outputted plural times at one frequency characteristics correction and the sound is collected by the microphone to execute averaging. Second, a predetermined interval is ensured after outputting of the test signal until the next output of the test signal in order to eliminate the effect of a reverberation. Third, it is necessary to perform a D/A conversion of the test signal and an A/D conversion of the collected test sound with a proper sampling frequency in order to properly output the test signal to the sound space as a test sound.